1. Field of the Invention
The present invention is related to a method of and apparatus for producing cutout mask data which are employed to extract or eliminate a cut-out area within an original image.
2. Description of Related Art
A typical picture of commodities used as an original for producing printed matter, such as a catalogue or the like, has a background other than the commodities themselves. The printed matter, in contrast usually shows only the commodities without the background.
A cutout mask is employed to remove the background area (or a cut-out area) from the original. The cutout mask is a film which is opaque in the cutout area and transparent in the remaining part of the original. A reproduced image without the background is produced by photographic reproduction while laying the cutout mask over the original or a fully-reproduced image of the original. Another type of cutout mask whose transparent and opaque portions are reversed is employed when the background is replaced with an other picture image.
In an image processing apparatus known as a color page make-up system, the cutout mask is treated as one of several images and is represented by image data (cutout mask data); the reproduced image without the background is represented by image data which are produced by processing the cutout mask data and original image data depicting the original. The method of producing cutout mask data in an image processing apparatus is described in the Japanese Patent Publication Gazettes Nos. 1985-13178 and 1985-5747 disclosed by the applicant of the present invention, for example.
The cutout mask data is usually produced by displaying the original image on a displaying device, and manually designating an outline of the cutout area within the original image with a digitizer or the like. Further, an image compression operation, which is performed by skipping pixels at regular intervals in the original to collect compressed image data, e.g., skipping pixels with interpolation and the like, may be applied in the production of the cutout mask data; this enables the displaying device to show the whole original image at a time when the total number of pixels in the original image is larger than that of the displaying device.
However, on the compressed image, the outline of the cutout area is hard to designate precisely because some of the pixels of the original image are omitted in the compressed image. In order to precisely designate the outline, a method in which a partial image of the original is displayed without image compression i.e., displayed at actual resolution is often applied. In this method, a plurality of partial images which cover the outline of the cutout area is first designated by an operator while the compressed image of the whole original is displayed. One of the plurality of partial images is displayed at actual resolution on the displaying device, and the operator designates a part of the outline; similar processing is repeated for all of the plurality of partial images. In a similar method, at every time the processing is finished for one partial image, the next partial image is specified on the compressed image, or the position of the next partial image is designated by a direction and a distance from the current position.
According to the foregoing conventional methods, an operator sometimes loses a relation between a part of the outline designated on the previous partial image and that designated on the current partial image. Further, because one partial image includes only a part of the cutout mask, it is sometimes difficult to locate the outline in it. Moreover, because the plurality of partial images are sequentially displayed, image data for respective partial images are inefficiently read out from a disc memory one by one to make a partial image; therefore, the process takes much time.